Safety device for fuses



April 14, 1970 LOHNERT ET AL 3,505,959

SAFETY DEVICE FOR FUSES Filed April 12, 1968 W n/r096 Job/barf [aim/[Pr United States Patent Office 3,505,959 SAFETY DEVICE FOR FUSES Adalbert Lohnert, Furth, Bavaria, and Hans Bedall,

Nuremberg, Germany, assignors to Diehl, Nuremberg, German Filed Apr. 12, 1968, Ser. No. 720,916 Claims priority, application Germany, Apr. 13, 1967,

D Int. Cl. F42c 9/ 08, J/08, 9/10 US. Cl. 102-70 7 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a safety device for fuses provided with pyrotechnic preparations, in which the detonator by means of a safety member is held in ineffective position preferably against the force of a spring, and occupies its live position only after fuse releasing means have been actuated.

For purposes of locking fuses, in addition to securing a firing pin or a striker in its starting position by means of shearable elements, ball stops, or the like, also the detonator by means of which the ignition is conveyed to the explosive charge, or a secondary charge is held in its rest location in an ineffective position. To this end, for instance, a body which carries the detonator cap is laterally displaceable or turnable against the thrust of a spring. For purposes of holding the detonator carrier in its starting position, there may also be used the ignition pin which extends into a bore of the detonator carrier and which, for instance, frees the latter only after the firing when an air braking effect is exerted by the inertia forces which act upon the pin. The detonator, serving for instance as primary charge, is in rest position displaced or turned relative to the secondary charge to such an extent that even if an accidental ignition of the detonator cap in this position should occur, the explosive charge will still not be initiated. With hand grenades and other ammunition which is thrown or fired without higher precisely defined acceleration, the locking with such heretofore known means is possible in view of the lack of a precisely determined time or a timewise defined correspondingly high torque for activating purposes.

In addition to the above mentioned fuses, also fuses are known which have a pyrotechnic time member which after the expiration of a predetermined time, brings the detonation of the grenade.

Furthermore, fuses have become known which are equipped with a thermal battery and in which electric energy is produced by a heating charge or preparation. By means of this energy, either during the impact or after the expiration of a predetermined time, the explosive charge is ignited through an initiating charge which will be electrically activated. The drawback of such fuses consists in that they have no means for de-activating the detonator. In other words, the detonator is from 3,505,959 Patented Apr. 14, 1970 the very start, i.e. already prior to the firing or throwing, in its activated condition.

It is, therefore, an object of the present invention to provide de-activating means for a fuse of the last mentioned type.

It is another object of this invention to provide an arrangement as set forth in the preceding paragraph which will include means for activating the detonator after the projectile has been in flight for a certain time.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing, in which: 7

FIGURE 1 illustrates a longitudinal section through a hand grenade fuse with a safety device according to the present invention;

FIGURE 2 is a longitudinal section through a somewhat modified fuse according to the invention.

The safety device according to the present invention is characterized primarily in that a fusible element serves as safety device which is located adjacent to the pyrotechnic preparation and is adapted by means of the latter to be heated up to a temperature at which it will soften or melt. Such an arrangement will by simple means assure a de-activation of the fuse prior tot he firing or throwing of the projectile or hand grenade and will assure that the hand grenade or projectile will remain de-activated for a predetermined time or distance while in flight.

Referring now to the drawing in detail, the fuse which by means of a threaded section 1 is inserted into the splinter carrier (not shown), and its bursting charge of a hand grenade comprises a head section 2 having a pivot 3 that links an arm 4 thereto. This arm 4 is held in its rest position by means of a safety pin 5 extending into a bore. One end of a leaf spring 6 extends through a bore 7" in the outwardly extending arm 2a of head section 2. Leaf spring 6 engages the arm 4 from the inside and continuously urges the arm 4 to pivot outwardly and to throw the said arm 4 away from the head section 2 in a manner known per se. Head section 2 has an ear section e with milled out slots 2 through which a pin p extends. In these slots and on said pin, there are sus pended bent extensions d.

The arm 2:: together with two side walls a forms a chamber c. Pivotally supported by the pivot 3 and located in chamber 0 is a hammer arm 7 which is springbiased by a spring 8. Spring 8 has one leg in engagement with the head section 2 while the other leg rests against the hammer arm 7 and thereby urges a hammer 9 of the arm 7 to engage the arm 4 or at the leaf spring 6 inserted therein. Thus also spring 8 contributes to the pivoting of arm 4 after the safety pin 5 has been pulled out and aids in throwing the arm 4 away from the head section 2.

After the safety pin 5 has been pulled and arm 4 has thus been released, leaf spring 6 arches outwardly and lifts arm 4. Leaf spring 6 then springs up and, under the the influence of hammer 9, hooks out of bore 1. Now hammer arm 7 is completely free. Therefore, after the arm and the spring plate 6 have been thrown off, the spring 8 is able to tilt the hammer arm 7 in counterclockwise direction until the hammer 9 impacts upon an ignition cap 10 which is centrally inserted into an ignition cap carrier 11. A bore 12 leads to an incendiary and heating charge or preparation 13 which is located in a housing 14. A helical spring 16 presses on one hand against a collar 15 of the housing 14 and on the other hand rests on the ignition cap carrier 11. The heating charge or preparation 13 is located in axial direction, but separated by a thin wall, followed by an ignition device which comprises, for instance, a piezoelectric cell 17 which when being subjected to heat furnishes a voltage, and also comprises a sealing closure 18, a spark gap 19, an electrode 20, a detonator carrier 21 firmly connected to the housing 14, for instance by grooves, and a detonator cap 22 adapted to be initiated electrically. According to the specific embodiment shown in the drawing, the ignition of the detonator is effected when the ignition voltage of the spark gap has been obtained. However, it is also possible to initiate the ignition of the detonator by means of an impact switch. Such switch for connecting the detonator cap 22 with the ignition current generator 17 which is designed for instance as all side impact contact, is not shown in the drawing.

The housing 14 and the members 13-22 are axially displ-aceable in a tube-shaped sleeve 23 the bottom of which has pressed therein a secondary charge 24 forming a so-called booster. Inserted into this charge 24 from the top is a cup 25 which has a relatively thick bottom and which has its inner dimensions correspond substantially to the outer dimensions of the detonator cap 22. Also the detonator cap 22 has a strong bottom and is so designed that the initiating jet or shock during the ignition of the detonator cap 22 spreads primarily in radial direction. The great distance between the detonator cap 22 and the secondary charge 24 will assure that at a premature ignition of the detonator cap 22 which may occur for instance when the heating and incendiary charge or preparation 13 is pierced, the detonator cap 22 will not transfer an ignition to the booster 24.

As safety member for securing the housing 14 and the elements 13, and 17-22 connected thereto in rest position, there is provided a connecting tube 26 which consists of a material which when heated up to a temperature as it is obtained by the burning heating charge or preparation 13, will soften and melt. Such material may be, for instance, synthetic resin or Woods metal.

A different solution to the problem underlying the present invention is illustrated in FIG. 2 in which those parts which correspond to the respective parts in FIG. 1 have been designated with the same reference numerals as in FIG. 1. Instead of an electric fuse, the arrangement of FIG. 2 has, adjacent to the heating charge or preparation, a firing charge or preparation 27 for the charges or preparations of a detonator cap 29 likewise inserted at the bottom of asleeve 28. The sleeve 28 is connected to a housing 30 which, in contrast to the arrangement of FIG. 1, has no fixed collar but is provided with an annular support 31 for the helical spring 16. Soldered to the spring 16, preferablys with Woods metal or another low melting solder, is a tubular body 32 having its upper flange 33 connected to the head section 2 while simultaneously serving at support for the other end of spring 16. As

melting fuse there is thus employed a soldering area 36. At the bottom of the outer sleeve 23, there is provided a secondary charge 34 into which is inserted a cup 35.

The operation of both safety devices will be evident from the drawing. When the hammer 9 impacts upon the cap 10, the heating charge or preparation 13 is ignited. When the heating charge or preparation burns, it heats up the melting element in the form of the tube 26 (FIG. 1) or the soldering area 36 (FIG. 2). As a result thereof, the helical spring 16, which up to this time was held under tension, will now be able to displace the carrier 14, 21; 30, 28 for the detonator cap 22, 29 from its safety position in downward direction. The detonator cap 22, 29 will thus be moved into the cup 25, 35 which means into the secondary charge 24, 34 and will then be in armed condition. When the detonator cap 22, 29 ignites, it initiates the secondary charge 24, 34 in view of the primarily radially effective ignition shock.

The arrangement according to the present invention will thus assure that in rest position the detonator cap 22, 29 is axially removed from the secondary charge 24, 34 as far as possible and that during a premature ignition of the detonator cap 22, 29 no initiation of the explosive charge occurs. When the heating charge or preparation 13 burns, delayed by the heating bridge, the safety element 26, 36 melts and frees the detonator carrier 14, 21; 30, 28 for the action of the spring 16. The detonator is then in armed condition,

The position of the melting element 26, 36 or its arrangement at the start or further below of the heating charge or preparation as well as the type of the heating bridge will determine the time after which, counting from the ignition of the cap 10, the detonator cap 22, 29 will reach its armed position or condition.

Instead of blocking the detonator against axial displacement from its safety position to its armed position by a melting element 26, 36 according to FIGS. 1 and 2, also a laterally disengageable, turnable or tiltable detonator carrier may be in its rest position secured, for instance, by a melting element in the form of a melting pill.

The melting element may, however, also be of a different shape and may, for instance, be designed as pin which will hold the two elements in their rest position which elements are by means of a spring force displaceable, disengageable, tiltable or turnable relative to each other. Furthermore, a soldering area could be provided at the separating gap of a, for instance, two-sectional housing at the abutting areas thereof, for instance between the parts 26 and 14.

It is, of course, to be understood that the present invention is, by no means, limited to the particular constructions shown in the drawing but also comprises any modifications that will appear to those skilled in the art.

What we claim is:

1. A fuse which includes: pyrotechnic means, means operable to ignite said protechnic means, detonator means arranged 'within the range of action of said pyrotechnic means, a secondary charge arranged in spaced relationship to said detonator means, said safety means normally holding said detonator means in its inactive position, and including means adapted to yield in response to-heat developed by said pyrotechnic means to thereby release said detonator means for action upon said secondary charge.

.-2. A fuse according to claim 1, which includes: spring means continuously urging said detonator means to act upon said secondary charge, and in which said means adapted to yield in response to heat developed by said pyrotechnic means is formed by a heat meltable member adapted when at normal ambient temperature to prevent said spring means from moving said detonator means into position for acting upon said secondary charge.

- 3. A fuse according to claim 2, in which said meltable member is made of an easily meltable material selected from the group consisting of soldering material and synthetic resin.

4. A fuse according to claim 2, which includes: housing means arranged in axial alignment with said pyrotechnic means and carrying said detonator means, said spring means being in the form of a coil spring continuously urging said housing means with said pyrotechnic means and said detonator means in the direction toward said secondary charge for igniting the same, but being prevented from moving said housing means and said pyrotechnic means toward said secondary charge until said heat meltable member has melted.

5. A fuse according to claim 4, which includes: a stationary member, and pin means forming said meltable member and connecting said detonator housing member to said stationary member.

6. A fuse according to claim 4, which includes: a stationary member, and tubular means forming said meltable member and connecting said detonator housing member to said stationary member.

7. A fuse according to claim 4, which includes: sleeve means substantially coaxial with said pyrotechnic means, that end portion of said sleeve which is closest to said detonator means being provided with annular abutment means adapted to engage and hold said spring means in loaded condition while being connected to said sleeve means by soldering material meltable by heat emanated from said pyrotechnic material, whereby with said soldering material in melted condition said spring means detaches said annular abutment means from said sleeve means and is free to displace said detonator means toward said secondary charge for firing the same,

References Cited UNITED STATES PATENTS BENJAMIN A. BORCHELT, Primary Examiner T. H. WEBB, Assistant Examiner US. Cl. X.R. 

